One conventional method for analyzing data obtained by a mass analysis is to use profile data, which shows a mass spectrum with an m/z value (mass-to-charge ratio) of ions detected in sequence and the detection intensity of them as data showing a mass spectrum as described in Non-Patent Documents 1 and 2. Profile data is a data form corresponding to raw data of a mass spectrometer. In the conventional mass analysis data analyzing method using the profile data, an isotopic cluster is first identified by analyzing the configuration of each peak on the profile data with a pattern recognition algorithm, and then, based on the result, the valence of each peak is determined and the monoisotopic peak is identified: where the isotopic cluster is a peak group consisting of a plurality of peaks which originate form ions having the same elemental composition yet have different m/z values depending on the difference of the isotopic composition of ions, and the monoisotopic peak is a peak of the ion which represents an isotopic cluster. Normally it is a peak of the ion consisting of the isotope having the largest natural abundance ratio.
[Non-Patent Document 1] Journal of the American Society for Mass Spectrometry, 2000, Vol. 11, pp. 320-332
[Non-Patent Document 2] Journal of the American Society for Mass Spectrometry, 1995, Vol. 6, pp. 229-233